1. Field of the Invention
The present invention relates to a pixel circuit and an organic light emitting display, and in particular, a pixel circuit connected to a plurality of organic light emitting diodes (OLEDs) that emit light so that it is possible to improve the aperture ratio of the light emitting display using such a pixel circuit.
2. Discussion of Related Art
Recently, flat panel displays have been developed, that are of reduced weight and volume as compared with displays using cathode ray tubes (CRT). Highlighted are organic light emitting displays having improved luminous efficiency, brightness, and view angle and high response speed.
An OLED has a structure in which an emission layer that may be a light emitting thin film is positioned between a cathode electrode and an anode electrode. Electrons and corresponding holes are injected into the emission layer so that they are recombined to generate exciters whose energy is reduced. As a result, light is emitted.
In the OLED, the emission layer is formed of either organic or inorganic material. Types of OLEDs are divided into an inorganic OLEDs and an organic OLEDs according to the emission layer material.
Referring to FIG. 1, four adjacent pixels are shown each that include an OLED and a pixel circuit. The pixel circuit includes a first transistor M1, a second transistor M2, a third transistor M3, and a capacitor Cst. The first, second, and third transistors M1, M2, and M3 each includes a gate, a source, and a drain. The capacitor Cst includes a first electrode and a second electrode.
Since the pixels have the same structure, the pixel shown in the upper left of FIG. 1 will be described. The source of the first transistor M1 is connected to a power source supply line Vdd, the drain is connected to the source of the third transistor M3, and the gate is connected to a first node A. The first node A is connected to the drain of the second transistor M2. The first transistor M1 supplies current corresponding to a data signal to the OLEDs.
The source of the second transistor M2 is connected to a data line D1, the drain is connected to the first node A, and the gate is connected to a first scan line S1. The second transistor M2 transmits the data signal to the first node A in accordance with the scan signal applied to the second transistor's gate.
The source of the third transistor M3 is connected to the drain of the first transistor M1, the drain is connected to the anode electrode of the OLED, and the gate is connected to an emission control line E1 to respond to an emission control signal. Therefore, the third transistor M3 controls the flow of current that flows from the first transistor M1 to the OLED in accordance with the emission control signal to control emission of the OLED.
The first electrode of the capacitor Cst is connected to the power source supply line Vdd while the second electrode is connected to the first node A. The capacitor Cst charges in accordance with the data signal and applies the data signal to the gate of the first transistor M1 for one frame for operation of the first transistor M1 over the frame.
However, according to the pixel used for a typical organic light emitting display, since an OLED is connected to each pixel circuit, a plurality of pixel circuits are necessary in order to emit light from a plurality of OLEDs.
Also, since one emission control line is connected to each pixel row, the aperture ratio of the organic light emitting display deteriorates.